Because first bid lists are matched to Choice #1 first. DEF could be filled by the time second choices are matched.

Computerized matching is a huge time saver but I think the methodology of bid matching was best learned by being there during hand matching. Essentially, they went through each PNM and called out the first choice. If she was on that group's first bid list, the person would say "Match" and everybody else would cross her off of their list. If she was on someone else's first list, then the first person on their second bid list would bump up to the first bid list.

After all first choices were read off one time, they went through them again, to see if anybody had been bumped up to the first bid list for their first choice. This continued until there were no matches for first choices. Then second choices would start. So, DEF may have filled up with women who put them first before Suzy PNM's second choice came up.